The present invention relates to an antenna assembly suitable for wireless transmission of analog and/or digital data, and more particularly to a highly compact broadband antenna assembly having a low specific absorption rate for use with wireless communication devices.
There are a variety of antennas which are currently used in wireless communication devices. One type of antenna is an external half wave single or multi-band dipole. This antenna typically extends or is extensible from the body of a wireless communication device in a linear fashion during normal operation. Because of the physical configuration of this type of antenna, it is relatively insensitive to directional signal optimization. In other words, it is able to operate in a variety of positions without substantial signal degradation and is considered omni-directional. This means that not only do electromagnetic waves radiate equally toward and away from such an antenna, they also radiate equally toward and away from a user of a wireless communication device equipped with such an antenna. There is essentially no front-to-back ratio (with respect to a wireless communication device) and little or no Specific Absorption Rate (SAR) reduction with this type of antenna. With multi-band versions of this type of antenna, where resonances are achieved through the use of inductor-capacitor (LC) traps, gains of +2 dBi are common.
While this type of antenna is acceptable in some wireless communication devices, it has drawbacks. One significant drawback is that the antenna is external to the body of the communication device. This places the antenna in an exposed position where it may be accidentally or deliberately damaged. Another drawback of increasing importance is due to the inherent omni-directionality of the antenna. That is, that which enables the antenna to operate optimally, may subject a user of a wireless communication device to unacceptable levels of electromagnetic radiation when the device is operated proximate a user.
A related antenna is an external quarter wave single or multi-band asymmetric wire dipole. This antenna operates much like the aforementioned antenna, but requires an additional quarter wave conductor to produce additional resonances and has drawbacks similar to the aforementioned half wave single or multi-band dipole antenna.
Another type of antenna is the internal single or multi band asymmetric dipole. This type of antenna usually features quarter wave resonant conductor traces, which may be located on a planar printed circuit board within the body of a wireless communication device. Such antennas typically operate over one or more frequency ranges with gains of +1-2 dBi. This antenna may include one or more feed points for multiple band operation, and may require a second conductor for additional band resonance.
Yet another antenna is an internal single or multi-band Planar Inverted xe2x80x9cFxe2x80x9d Antenna (PIFA). This type of antenna features a single or multiple resonant planar conductor that operates over a second conductor or ground plane. With this type of antenna, gains of +1.5 dBi are typical.
Another type of antenna is a patch antenna. The patch antenna is a small, low profile antenna which is useful in wireless communication devices. They typically have operating bandwidths (2:1 Standing Voltage Wave Ratio) on the order of a few percent. The operating bandwidth may be increased by adding parasitic elements. However, the total size of the antenna increases proportionately. The front to back ratio is usually poor unless the ground plane size is also increased. Thus, in creating a patch antenna with a relatively large bandwidth, the primary advantage of the patch antenna is defeated.
Each of these known various antenna structures have limitations, including a decrease in operational efficiency when positioned near a user""s head. As a result, there exists a need for a broadband antenna assembly which is compact and lightweight. Yet another need exists for an unitary antenna structure having a wide bandwidth without a separate antenna structure for each transmission and reception band. Still another need exists for an antenna having reduced SAR. There is a need for an antenna assembly which may be incorporated into a variety of wireless communication devices. There is also a need for an antenna assembly with a reduced specific absorption rate.
A broadband antenna assembly having a low specific absorption rate for use with a wireless communication device. The antenna assembly includes a driven element and parasitic element, operatively connected to a radio frequency input/output port and a ground plane, such as provided by the printed circuit board of the communication device. The driven element may take the form of a first trace on a suitable substrate or take the form of a first body member, while the parasitic element may take the form of a second trace on a suitable substrate or take the form of a second body member. Importantly, the overall length of both the driven and parasitic element is substantially less than xc2xcxcex.
In the first embodiment, the first and second traces are formed on one side of a suitable substrate such as a printed circuit board which is then superposed above a predetermined region of a ground plane by connector members. Generally, the first trace has two ends, with one end having a feed point to which a first connector member is attached, while the second trace has a plurality of segments with ends, with one of the ends having a ground connection point to which a second connector member is attached. The first and second connector members operatively couple the first trace to an input/output port and the second trace to the ground plane, respectively. Preferably, the input/output port is adjacent to and in a fixed position relative to the ground plane to enable the connector members to align and support the substrate and the traces. For optimum operation, the first and second traces are spaced apart from each other by a distance that establishes proper coupling to the frequency band of operation. As a result, a compact high bandwidth antenna is provided.
In the second embodiment of the antenna assembly, the first and second body members are superposed above a predetermined region of a ground plane by connector members. Generally, the first body member has a plurality of segments with one end operatively connected by a first connector member to an input/output port, while the second body member has a plurality of segments and with one end operatively connected by a second connector member to a ground plane. Preferably, the input/output port is adjacent to and in a fixed position relative to the ground plane to enable the first connector member to align and support the first body member. The opposite ends of both the first and second body members includes an arm member which extends toward the ground plane. More specifically, the first and second body members are co-planar with their respective arm members and having roughly the same extension toward the ground plane. Preferably, the second body member comprises two segments which form a predetermined angle with the apex of the angle proximate the first body member. As with the aforementioned first embodiment or form, the first and second body members are spaced from each other by a distance related to the frequency of operation.
In a third embodiment, the first and second body members of the aforementioned second embodiment may be used as a feed system for an auxiliary antenna element, with the auxiliary antenna element comprising a dielectric member and a conductor element. Preferably, the auxiliary antenna element is superposed above and adjacent to the first and second body members of the aforementioned second embodiment. In use, the auxiliary antenna element extends the bandwidth of the first and second body members. In another embodiment, the antenna may be manufactured as a plated or foil conductive material imprinted or disposed upon a dielectric substrate using known printed circuit fabrication techniques. In the third embodiment, the aforementioned body members of the second embodiment of the antenna assembly are used in conjunction with an auxiliary antenna element. Said auxiliary antenna element may be composed of a metallic plate supported by a dielectric substrate which provides the proper spacing to the antenna feed system and the ground plane element which may be the ground plane of the printed wiring board of a communication device.
In a fourth embodiment, a multiple band antenna assembly is provided. In an illustrated embodiment, the antenna assembly includes a plurality of stacked antenna elements, each defined with respect to a different frequency band of operation. Additionally, the stacked antenna elements may be disposed in substantially parallel relationship with each other.
As with all of the embodiments, it will be appreciated that various componentry may be positioned within the open space(s) between the antenna assembly and the ground plane to facilitate compact construction.
It is an object of the present invention to provide an antenna assembly which may be incorporated into a wireless communication device.
Another object of the present invention to enhance operation of an antenna assembly by increasing its operational bandwidth.
A feature of the present invention is that there is a single feed point for multiple electromagnetic frequency ranges or bands.
Another feature of the present invention is that fabrication may be accomplished through existing technologies and mass production techniques.
Yet another feature of the present invention is the provision of a low specific absorption rate (SAR) antenna.
An advantage of the present invention is that the antenna assembly has a low profile which enables it to be used in small articles such as wireless communication devices.
Another advantage of the present invention is that various components of a transceiver device may be positioned within interior regions of the antenna assembly to reduce the overall size of the electronic device.
Yet another advantage of the present invention is that a multiple band antenna may be implemented having a plurality of individual antenna structures, each structure associated with a given frequency band of operation. In one preferred embodiment, the plurality of individual antenna structures may be stacked in a substantially parallel manner.
These and other objects, features and advantages will become apparent in light of the following detailed description of the preferred embodiments in connection with the drawings.